1. The Field of the Invention
The present invention relates to medical devices having a composite coating on at least a portion of the medical device.
2. The Relevant Technology
Surgical site infection (“SSI”) (also referred to as post-operative infection or perioperative infection) is a major factor contributing to patient morbidity and mortality. A SSI is an infection that occurs after surgery in the part of the body where the surgery took place. Some of the common symptoms of SSI include: redness and pain around the surgical area, drainage of cloudy fluid from the surgical wound, and postoperative fever. SSIs contribute to longer hospital stays, longer rehabilitation times, greater antibiotic usage, higher patient expenses, and higher hospital expenses. In extreme cases, SSIs can lead to patient death.
Most patients who have surgery do not develop an infection. Nevertheless, some form of infection is associated with about 38% of surgical procedures. Between 5% and 50% of open fractures result in SSI and about 1-3% of elective procedures, which includes most joint replacement procedures, result in SSI. The organisms commonly associated with SSI include, but are not limited to, staphylococci and pseudomonads.
Doctors and hospitals employ a number of techniques to prevent SSI including, but not limited to, use of sterile technique and protective clothing, thorough cleaning of the surgical site prior to the procedure, and antibiotic prophylaxis (i.e., treatment with antibiotics prior to surgery). Antibiotic prophylaxis with standard antibiotics (e.g., penicillin and the like) is, however, controversial due to the fact that its effectiveness is questionable and it is believed that it may contribute to antibiotic resistance.
Even when sterile techniques are adhered to, surgical procedures can introduce bacteria and other microbes into the patient's body, which can colonize and infect different parts of the body. Antibiotics can be effective in treating such infections. However, once established in the patient's body, many SSIs can be resistant to antibiotic treatment. For example, many SSIs are associated with biofilm formation; biofilms are antibiotic-resistant aggregates of microorganisms in which cells adhere to each other on a surface. Many indwelling medical devices (e.g., catheters, replacement heart valves, joint replacement prostheses) are particularly susceptible to biofilm formation.
One technique that has been explored for preventing biofilm formation and other SSIs associated with these devices is to coat them with antibiotics. However, most antibiotics are readily soluble in water and their effectiveness can be diminished or eliminated if they are washed away or diluted. As a result, most antibiotics are generally not very effective for inhibiting microbial growth on surfaces. One technique that has been explored for making antibiotics more active on surfaces (e.g., polymer surfaces) is to covalently attach the antibiotic to the surface. For example, U.S. Pat. No. 7,854,941 to Urban et al. describes a system for covalently attaching antibiotics (e.g., β-lactam antibiotics) to reactive moieties that are themselves covalently attached to a polymer surface. By selecting appropriate antibiotics, growth of both Gram-negative and Gram-positive bacteria on the polymer surface can be inhibited by such a system.